Optical fiber cables having optical-fiber modules are known from French Patent No. 2,665,266 (and its counterpart U.S. Pat. No. 5,155,789) and French Patent No. 2,706,218 (and its counterpart U.S. Pat. No. 5,671,312). Each of these patents is each hereby incorporated by reference in its entirety.
A conventional telecommunication cable can include a plurality of optical fibers that are grouped in modules to form a cable core (i.e., within the central cavity formed by the cable jacket). A module can contain between about 2 and 24 optical fibers that are enveloped in a thin, flexible retaining enclosure (i.e., the module's jacket). Such retaining enclosures and the enclosed optical fibers can be colored to facilitate identification of the optical fibers (e.g., during a connection operation).
With the development of optical fiber telecommunication systems to the subscriber (e.g., FTTH—“Fiber-To-The-Home” or FTTC—“Fiber-To-The-Curb”), high-capacity cables containing a large number of optical fibers grouped in modules are sought. Such cables must allow access to each module for distribution not only into a particular building but also into a particular floor within that building. To this end, operators carry out a dropping operation on the telecommunication cable in which an opening is made in the cable and one or more modules are withdrawn in order to supply a signal to a given optical system.
International Publication No. WO 01/98810 A1 (and its counterpart U.S. Pat. No. 6,718,101), each of which are hereby incorporated by reference in its entirety, describe an ovalized optical cable with continuous accessibility. The disclosed cable, which is suitable for subscriber local loops and inside cabling, includes a protective jacket receiving optical-fiber modules. The disclosed cable can accommodate approximately 12 to 96 optical fibers, which are arranged in the cable so as to occupy much of the cavity along the cavity's major axis but to leave significant clearance in the cavity's minor axis. This clearance allows variations in the overlength of the fibers within the cable. Reinforcing elements are positioned within the protective jacket on either side of the cavity along the cavity's major axis. The cable can be wound onto a cable drum or bent during installation in a conduit along the cavity's major axis, thus taking advantage of the significant clearance in the cavity's minor axis. The optical-fiber modules are loosely positioned within the cavity, allowing stresses to be eliminated during extension of the cable jacket under a certain tension or under the effect of thermal expansion or contraction. The cable jacket includes markings (e.g., colored threads, fracture initiators, or regions of lower thickness) to indicate the regions where windows could be cut for dropping operations. A first access window can thus be opened to cut a given module and a second access window can be opened to extract the selected module.
U.S. Pat. No. 7,272,282, which is hereby incorporated by reference in its entirety, describes a flat cable in which optical fibers are freely positioned in buffer tubes, which are loosely arranged in a ribbon-like array in the cable. Although the buffer tubes can be extracted from the cable, extracting fibers from the buffer tubes would subject the optical fibers to unwanted stresses. Moreover, the extraction of optical fibers from the cable would require a cutting tool.
European Patent Application No. 0,569,679 A1, which is hereby incorporated by reference in its entirety, discloses a flat cable having optical fibers freely positioned in metal tubes. Although this publication does not describe the manner in which the fibers would be extracted during a dropping operation, access to the optical fibers through the metal tubes would be difficult.
When the foregoing conventional cables are vertically positioned, however, the constituent modules sag within the cable. This can cause buckling of the micromodules below and corresponding tension upon the micromodules above. These effects can cause unwanted attenuation. In addition, the optical fibers can be subjected to mechanical strains at the dropping points, thereby further increasing attenuation.
Therefore, a need exists for a cable having optical-fiber micromodules that can be installed vertically without the micromodules sagging within the cable and which facilitates easy dropping of the optical fibers.